Filter mask



FIG. 1 is a front view of the filter mask, the rear view being a mirror image thereof;

FIG. 2 is a top view of the filter mask;

FIG. 3 is a bottom view of the filter mask;

FIG. 4 is a left side view of the filter mask; and,

FIG. 5 is a right side view of the filter mask. 

The ornamental design for a filter mask, as shown. 